Longitudinal Analysis of Respiratory Syncytial Virus in Children During and After COVID-19 Pandemic: Shifts in Seasonality and Disease Burden

Abstract Background Non-pharmaceutical interventions (NPIs) against COVID-19 globally altered RSV seasonality, yet longitudinal evidence on age-specific severity changes remains scarce in China. Methods In this hospital-based surveillance study, 21,744 children hospitalized with acute respiratory infections (ARI) were enrolled. RSV was detected via RT-PCR across three phases: pre-pandemic (2017–2019), NPIs implementation (2020–2022), and post-NPIs (2023–2024). Results RSV positivity varied significantly between phases (p < 0.001), peaking at 37.83% (751/1,985) in 2021. Seasonal peaks shifted from winter (pre-pandemic) to spring (post-NPIs). The disease burden shifted toward infants aged 7–12 months (38.46%, 845/2,197 vs. 20.45%, 200/978 pre-pandemic; p < 0.001). Notably, mechanical ventilation was required in 8.00% (4/50) and 5.71% (2/35) of severe pneumonia cases aged 13–36 months during Phases II and III, respectively, whereas no cases were recorded pre-pandemic (0/14; p = 0.85). Conclusion NPIs fundamentally reshaped RSV epidemiology, inducing seasonal shifts and redirecting disease burden toward older infants experiencing delayed primary infection due to "immune debt."